In order to maintain quality control of fresh concrete as delivered to a job site and to determine compliance with specifications under which the concrete is furnished, usual testing procedures require the taking of samples of the concrete material as it is delivered from the concrete mixer. The concrete samples are used for compression test cylinders and also for measuring the consistency or slump of the delivered concrete material.
The handling of such samples of concrete material for conducting such tests are set forth by the American Society for Testing Materials in their specifications ANSI/ASTM C 172-171 and the standard test method for slump of concrete in ANSI/ASTM C 143-78. ASTM methods require that two samples be taken from the center portion of the load over a period not to exceed 15 minutes. These two samples are then to be combined and reconstituted; i.e., thoroughly mixed with a shovel in a wheel-barrow to assure uniformity, the test to be started within five minutes and completed within two and one-half minutes. A probable elapsed time of 20.+-. minutes by which time the truck may be completely discharged providing no timely basis for rejection and therefore no control of the load in question and only vague correlation with the next succeeding loads.
It will be apparent that determining the slump in this manner as it has been done for approximately 50 years or more provides slump data available to the quality control person on the job only after the load has been placed in its final location or form. There is little opportunity at the conclusion of testing to redirect the discharge flow of the concrete or modify the mixture of the concrete material being delivered, since the load being tested is often easily discharged by the time the test has been made. If the delivered concrete material does not meet the slump specified, remedial steps must be taken on succeeding loads based on still further testing.
It will be apparent that job sites impose various conditions upon the manner in which ready mixed concrete material can be delivered to its final location. Such conditions often make the taking of samples of the concrete in accordance with ASTM specifications difficult and sometimes cause serious interruption of the concreting operations. To obtain indication of the slump of concrete being delivered, it has been proposed that measurement of slump of the concrete be taken by devices placed on the mixing drum to measure the consistency of the concrete material within the drum. Such prior proposed devices are shown in U.S. Pat. Nos. 2,821,079, 1,730,893, 2,013,837, 3,640,121 and 3,924,447.
Other prior proposed devices for controlling consistency of a flowable material have included a vane or a blade insertable into a flow path of material, the vane or blade being connected to a torsion means mounted outside of the conduit or receptacle in which the material was moving. Such prior devices are shown in U.S. Pat. Nos. 3,364,730, 4,148,215, 2,629,790, 3,147,612 and 3,027,756.